Method and apparatus for block vector prediction with integer offsets in intra picture block compensation

ABSTRACT

A method of video decoding performed by a video decoder includes receiving a coded video bitstream containing a current picture. The method includes determining whether a current block in the current picture is coded in intra block copy (IBC) mode. The method includes in response to a determination that the current block is coded in IBC mode, determining whether a mode with a motion vector offset is enabled for the IBC encoded current block. The method further includes in response to a determination that the mode with the motion vector offset is enabled for the IBC encoded current block, decoding the current block in accordance with an offset associated with the current block. Furthermore, the fractional offsets are not permitted for the IBC encoded current block.

INCORPORATION BY REFERENCE

This present application is a continuation Application of U.S.application Ser. No. 16/742,684 filed Jan. 14, 2020, which is claims thebenefit of priority to U.S. Provisional Application No. 62/792,892,“BLOCK VECTOR PREDICTION WITH INTEGER OFFSETS IN INTRA PICTURE BLOCKCOMPENSATION” filed on Jan. 15, 2019, which is incorporated by referenceherein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using. The order of forming acandidate list may be A0→B0→B1→A1→B2

SUMMARY

According to an exemplary embodiment, a method of video decodingperformed by a video decoder includes receiving a coded video bitstreamcontaining a current picture. The method further includes determiningwhether a current block in the current picture is coded in intra blockcopy (IBC) mode. The method further includes, in response to adetermination that the current block is coded in IBC mode, determiningwhether a mode with a motion vector offset is enabled for the IBCencoded current block. The method further includes, in response to adetermination that the mode with the motion vector offset is enabled forthe IBC encoded current block, decoding the current block in accordancewith an offset associated with the current block. Furthermore,fractional offsets are not permitted for the IBC encoded current block.

According to an exemplary embodiment, a video decoder for video decodingincludes processing circuitry configured to receive a coded videobitstream containing a current picture. The processing circuitry isfurther configured to determine whether a current block in the currentpicture is coded in intra block copy (IBC) mode. The processingcircuitry is further configured to, in response to a determination thatthe current block is coded in IBC mode, determine whether a mode with amotion vector offset is enabled for the IBC encoded current block. Theprocessing circuitry is further configured to, in response to adetermination that the mode with the motion vector offset is enabled forthe IBC encoded current block, decode the current block in accordancewith an offset associated with the current block. Furthermore, thefractional offsets are not permitted for the IBC encoded current block.

According to an exemplary embodiment, a non-transitory computer readablemedium, having instructions stored therein, which when executed by amethod of video decoding performed by a video decoder includes receivinga coded video bitstream containing a current picture. The method furtherincludes determining whether a current block in the current picture iscoded in intra block copy (IBC) mode. The method further includes, inresponse to a determination that the current block is coded in IBC mode,determining whether a mode with a motion vector offset is enabled forthe IBC encoded current block. The method further includes, in responseto a determination that the mode with the motion vector offset isenabled for the IBC encoded current block, decoding the current block inaccordance with an offset associated with the current block.Furthermore, fractional offsets are not permitted for the IBC encodedcurrent block.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of intra picture block compensationin accordance with an embodiment.

FIGS. 9A-9D is a schematic illustration of intra picture blockcompensation with one coding tree unit (CTU) size search range inaccordance with an embodiment.

FIGS. 10A-10D is a schematic illustration of how a buffer is updated inaccordance with an embodiment.

FIG. 11 is a schematic illustration of determining starting points attwo reference pictures associated with two reference picture lists basedon motion vectors of a merge candidate in a merge with motion vectordifference (MMVD) mode in accordance with an embodiment.

FIG. 12 is a schematic illustration of predetermined points surroundingtwo starting points that are to be evaluated in the MMVD mode inaccordance with an embodiment.

FIG. 13 is an illustration of an example decoding process in accordancewith an embodiment.

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

Block based compensation from a different picture may be referred to asmotion compensation. Block compensation may also be done from apreviously reconstructed area within the same picture, which may bereferred to as intra picture block compensation, intra block copy (IBC),or current picture referencing (CPR). For example, a displacement vectorthat indicates an offset between a current block and the reference blockis referred to as a block vector. According to some embodiments, a blockvector points to a reference block that is already reconstructed andavailable for reference. Also, for parallel processing consideration, areference area that is beyond a tile/slice boundary or wavefrontladder-shaped boundary may also be excluded from being referenced by theblock vector. Due to these constraints, a block vector may be differentfrom a motion vector in motion compensation, where the motion vector canbe at any value (positive or negative, at either x or y direction).

The coding of a block vector may be either explicit or implicit. In anexplicit mode, which is sometimes referred to as (Advanced Motion VectorPrediction) AMVP mode in inter coding, the difference between a blockvector and its predictor is signaled. In the implicit mode, the blockvector is recovered from the block vector's predictor, in a similar wayas a motion vector in merge mode. The resolution of a block vector, insome embodiments, is restricted to integer positions. In otherembodiments, the resolution of a block vector may be allowed to point tofractional positions.

The use of intra block copy at the block level may be signaled using ablock level flag, referred to as an IBC flag. In one embodiment, the IBCflag is signaled when a current block is not coded in merge mode. TheIBC flag may also be signaled by a reference index approach, which isperformed by treating the current decoded picture as a referencepicture. In HEVC Screen Content Coding (SCC), such a reference pictureis put in the last position of the list. This special reference picturemay also be managed together with other temporal reference pictures inthe DPB. IBC may also include variations such as flipped IBC (e.g., thereference block is flipped horizontally or vertically before used topredict current block), or line based (IBC) (e.g., each compensationunit inside an M×N coding block is an M×1 or 1×N line).

FIG. 8 illustrates an embodiment of intra picture block compensation(e.g., intra block copy mode). In FIG. 8, a current picture 800 includesa set of block regions that have already been coded/decoded (i.e., graycolored squares) and a set of block regions that have yet to becoded/decoded (i.e., white colored squares). A block 802 of one of theblock regions that have yet to be coded/decoded may be associated with ablock vector 804 that points to another block 806 that has previouslybeen coded/decoded. Accordingly, any motion information associated withthe block 806 may be used for the coding/decoding of block 802.

In some embodiments, the search range of the CPR mode is constrained tobe within the current CTU. The effective memory requirement to storereference samples for CPR mode is 1 CTU size of samples. Taking intoaccount the existing reference sample memory to store reconstructedsamples in a current 64×64 region, 3 more 64×64 sized reference samplememory are required.

In FIG. 9A, the upper left region of CTU 900 is the current region beingdecoded. When the upper left region of CTU 900 is decoded, the entry [1]of the reference sample memory is overwritten with the samples from thisregion, as illustrated in FIG. 10A (e.g., over-written memorylocation(s) has diagonal cross-hatching). In FIG. 9B, the upper rightregion of CTU 900 is the next current region being decoded. When theupper right region of CTU 900 is decoded, the entry [2] of the referencesample memory is overwritten with the samples from this region, asillustrated in FIG. 10B. In FIG. 9C, the lower left region of CTU 900 isthe next current region being decoded. When the lower left region of CTU900 is decoded, the entry [3] of the reference sample memory isoverwritten with the samples from this region, as illustrated in FIG.10C. In FIG. 9D, the lower right region of CTU 900 is the next currentregion being decoded. When the lower right region of CTU 900 is decoded,the entry [3] of the reference sample memory is overwritten with thesamples from this region, as illustrated in FIG. 10D.

According to some embodiments, a method called ultimate motion vectorexpression (UMVE, or called MMVD) includes a special merge mode in whichan offset on top of the existing merge candidates is signaled. Theoffset may specify both a magnitude and a direction. In UMVE (or MMVD),a few syntax elements are signaled to describe such an offset including,but not limited to:

Prediction Direction IDX: to indicate which of the prediction directions(L0, L1 or L0 and L1) is used for UMVE mode.

-   -   (ii) Base Candidate IDX: to indicate which of the existing merge        candidates is used as the start point to apply the offset.    -   (iii) Distance IDX: to indicate how large the offset is from the        starting point (along x or y direction, but not both). The        offset magnitude is chosen from a fix number of selections.    -   (iv) Search Direction IDX: to indicate the direction (x or y, +        or − direction) to apply the offset.

If the starting point MV is MV_S, the offset may be MV_offset.Accordingly, the final MV predictor may be MV_final=MV_S+MV_offset. InUMVE (or MMVD), the offset added to the base vector may be onedimensional. For example, only the x or the y direction may be appliedwith an offset value, but not both. The original offset distance table(in integer samples) is designed as the following 8 entries in Table 1:

TABLE 1 Distance_idx Distance[ x0 ][ y0 ] when [ x0 ][ y0 ] slicefracmmvd flag is equal to 1 0 ¼ 1 ½ 2 1 3 2 4 4 5 8 6 16 7 32

A slice level flag slice_fracmmvd_flag may be used to control theresolution of the offsets in Table 1. If this flag is equal to 1, theoffsets in Table 1 may be used. However, if this flag is equal to 0, allthe entries in Table 1 may be left shifted by 2 to make all entriesbecome integer positions, as illustrated in Table 2. The binarization ofa distance index may be fixed length coding using 3 bits.

TABLE 2 mmvd_distance_idx MmvdDistance[ x0 ][ y0 ] when [ x0 ][ y0 ]slice fracmmvd flag is equal to 0 0 1 1 2 2 4 3 8 4 16 5 32 6 64 7 128

FIGS. 11 and 12 illustrate an embodiment of a search process and searchpoint UMVE (or MMVD). As shown in FIGS. 11 and 12, a first motion vector(1111) and a second motion vector (1121) belonging to a first mergecandidate are shown. The first merge candidate can be a merge candidateon a merge candidate list constructed for the current block (1101). Thefirst and second motion vectors (1111) and (1121) can be associated withtwo reference pictures (1102) and (1103) in reference picture lists L0and L1, respectively. Accordingly, two starting points (1122) and (1124)in FIG. 11 can be determined at the reference pictures (1102) and(1103).

In an example, based on the starting points (1122) and (1124), multiplepredefined points extending from the starting points (1122) and (1124)in vertical directions (represented by +Y, or −Y) or horizontaldirections (represented by +X and −X) in the reference pictures (1102)and (1103) can be evaluated. In one example, a pair of points mirroringeach other with respect to the respective starting point (1122) or(1124), such as the pair of points (1214) and (1224), or the pair ofpoints (1215) and (1225), can be used to determine a pair of motionvectors which may form a motion vector predictor candidate for thecurrent block (1101). Those motion vector predictor candidatesdetermined based on the predefined points surrounding the startingpoints (1211) or (1221) can be evaluated.

In addition to the first merge candidate, other available or valid mergecandidates on the merge candidate list of the current block (1101) canalso be evaluated similarly. In one example, for a uni-predicted mergecandidate, only one prediction direction associated with one of the tworeference picture lists is evaluated.

Based on the evaluations, a best motion vector predictor candidate canbe determined. Accordingly, corresponding to the best motion vectorpredictor candidate, a best merge candidate can be selected from themerge list, and a motion direction and a motion distance can also bedetermined. For example, based on the selected merge candidate and Table2, a base candidate index can be determined. Based on the selectedmotion vector predictor, such as that corresponding to the predefinedpoint (1215) (or (1225)), a direction and a distance of the point (1215)with respect to the starting point (1211) can be determined. Accordingto Table 3 and Table 4 (reproduced below), a direction index and adistance index can accordingly be determined.

It is noted that the examples described above are merely forillustrative purpose. In alternative examples, based on the motionvector expression method provided in the MMVD mode, the motion distancesand motion directions may be defined differently. In addition, theevaluation process (search process) may be performed differently. Forexample, for a bi-prediction merge candidate, three types of predictiondirections (e.g., L0, L1, and L0 and L1) may be evaluated based on a setof predefined distances and directions to select a best motion vectorpredictor. For another example, a uni-predicted merge candidate may beconverted by mirroring or scaling to a bi-predicted merge candidate, andsubsequently evaluated. In the above examples, an additional syntaxindicating a prediction direction (e.g., L0, L1, or L0 and L1) resultingfrom the evaluation process may be signaled.

As described above, merge candidates on a merge candidate list areevaluated to determine a base candidate in the MMVD mode at an encoder.At a decoder, using a base candidate index as input, a motion vectorpredictor can be selected from a merge candidate list. Accordingly, noadditional line buffer is needed for the MMVD mode in addition to a linebuffer for storage of the merge candidates.

In intra block copy, a MMVD method may be applied to block vectorpredictions. A merge candidate of IBC can also apply an offset toincrease block vector predictors. However, the MMVD method for intermotion compensation involves fractional-pel offset values, which makethe direct application of inter MMVD to intra block copy infeasible.Embodiments of the present disclosure provide the significantlyadvantageous features of enabling intra block copy with MMVD in anefficient way.

The embodiments of the present disclosure may be used separately orcombined in any order. Further, each of the methods, encoder, anddecoder according to the embodiments of the present disclosure may beimplemented by processing circuitry (e.g., one or more processors or oneor more integrated circuits). In one example, the one or more processorsexecute a program that is stored in a non-transitory computer-readablemedium. According to embodiments of the present disclosure, the termblock may be interpreted as a prediction block, a coding block, or acoding unit (i.e., CU). A BV predictor may be a merge/skip modecandidate, or a BV with difference coding for the AMVP mode.

According to some embodiments, when the IBC mode uses MMVD, the offsetsapplied to an IBC base BV predictor are integer values. In this regard,fractional offsets are not permitted for the IBC mode. Preventingfractional offsets from being used in the IBC mode may be implemented bynot signaling a flag that indicates that fractional offsets are used, oralways treating this type of flag as false even when the flag issignaled. For example, when a high level IBC enable flag (e.g., SPS,PPS, slice, tile group, tile, etc.) is set to be true (IBC is used atthis level), the value of a slice level (or other level such as tilegroup or tile) flag slice_fracmmvd_flag will not be signaled, butinferred to be false (i.e., do not use fractional offsets in IBC mode).In another example, when the high level IBC enable flag is set to betrue, the slice_fracmmvd_flag is signaled as false.

According to some embodiments, a slice (or tile group) level flagslice_ibc_enabled_flag is signaled first, before the slice (or tilegroup) level flag for MMVD offset resolution (slice_fracmmvd_flag) issignaled. When the slice_ibc_enabled_flag is equal to 1 (IBC is used),the mmvd fractional flag slice_fracmmvd_flag is inferred to be 0 withoutsignaling. In another example, when the slice_ibc_enabled_flag is equalto 1 (IBC is used), the mmvd fractional flag slice_fracmmvd_flag issignaled as false. When slice_ibc_enabled_flag is 0 (IBC is not used),slice_fracmmvd_flag may be signaled to be either 1 or 0. This embodimentassumes MMVD method is always enabled for both IBC mode and regularinter mode.

According to some embodiments, a slice (or tile group) level flagslice_ibc_enabled_flag is signaled first, before the slice (or tilegroup) level flag for MMVD offset resolution (slice_fracmmvd_flag). Whenthe slice_ibc_enabled_flag is equal to 1 (IBC is used), and whenhl_ibcmmvd_flag is equal to 1 (i.e., MMVD is for IBC), the mmvdfractional flag slice_fracmmvd_flag is inferred to be 0 withoutsignaling. In another example, when both hl_ibcmmvd_flag andslice_fracmmvd_flag are equal to 1, the slice_fracmmvd_flag is signaledas false. If the slice_ibc_enabled_flag is 0 (IBC is not used) orhl_ibcmmvd_flag is equal to 0 (i.e., MMVD is not used for IBC), theslice_fracmmvd_flag is signaled to be either 1 or 0. This embodimentassumes that the MMVD method is always enabled for regular inter mode,but optional for IBC mode by a high level enabling flag hl_ibcmmvd_flag.This flag can be signaled at the same level as slice_ibc_enabled_flag oreven higher, such as at the SPS level.

According to some embodiments, a slice (or tile group) level flagslice_ibc_enabled_flag is signaled first, before the slice (or tilegroup) level flag for MMVD offset resolution (slice_fracmmvd_flag). Whenthe slice_ibc_enabled_flag is equal to 1 (i.e., IBC is used),hl_ibcmmvd_flag is equal to 1 (i.e., MMVD for IBC is used), andhl_mmvd_enabled_flag is equal to 1 (i.e., MMVD for inter is used), themmvd fractional flag slice_fracmmvd_flag is inferred to be 0 withoutsignaling. In another example, when slice_ibc_enabled_flag is equal to 1(i.e., IBC is used), hl_ibcmmvd_flag is equal to 1, andhl_mmvd_enabled_flag is equal to 1, the mmvd fractional flagslice_fracmmvd_flag is signaled but treated as false regardless of thevalue of slice_fracmmvd_flag. If slice_ibc_enabled_flag is 0 (i.e., IBCis not used) or hl_ibcmmvd_flag is equal to 0 (i.e., MMVD for IBC isused), but hl_mmvd_enabled_flag is equal to 1 (mmvd for inter is used),slice_fracmmvd_flag is signaled to be either 1 or 0. This embodimentassumes MMVD method can be optionally enabled for both IBC mode andregular inter mode by high level enabling flags hl_ibcmmvd_flag andhl_mmvd_enabled_flag. These two flags can be signaled at the same levelas slice_ibc_enabled_flag/slice_fracmmvd_flag or even higher, such as atthe SPS level.

According to some embodiments, when slice_fracmmvd_flag is equal to 0(i.e., only integer pixel offsets are used), the MMVD distance table inthe above disclosed embodiments will be different than the table inwhich the offsets are shifted by bits to convert the fractional offsetsto integer offsets. Instead, another table, which may include adifferent number of entries) is used when the slice_fracmmvd_flag isequal to 0. Table 3 illustrates an example table that may be used whenslice_fracmmvd_flag is equal to 0.

TABLE 3 mmvd_distance_idx MmvdDistance[ x0 ][ y0 ] when [ x0 ][ y0 ]slice fracmmvd flag is equal to 0 0 1 1 4 2 8 3 16 4 32 5 64 6 128 7 256

Table 4 illustrates another example table that may be used whenslice_fracmmvd_flag is equal to 0.

TABLE 4 mmvd_distance_idx MmvdDistance[ x0 ][ y0 ] when [ x0 ][ y0 ]slice fracmmvd flag is equal to 0 0 1 1 2 2 4 3 8

Because the number of entries can be different from the case whenslice_fracmmvd_flag is equal to 1, the binarization of the table mayalso be different. In this embodiment, 2 bits of fixed length coding maybe used.

FIG. 13 illustrates an embodiment of a process performed by a videodecoder such as video decoder (710). The process may generally start atstep (S1300) where a coded video bitstream including a current pictureis received. The process proceeds to step (S1302) where it is determinedwhether a current block included in the current picture is coded in IBCmode. If the current block is not coded in IBC mode, the processproceeds to step (S1304) where the current block is decoded inaccordance with a coding mode of the current block. For example, thecurrent block may be coded in accordance with an inter prediction modeor an intra prediction mode.

If the current block is coded in the IBC mode, the process proceeds fromstep (S1302) to step (S1306) where it is determined whether a mode withmotion vector offsets is enabled for the current block. For example, amode with motion vector offsets includes the MMVD mode. Furthermore, forexample, the mode with motion vector offsets may be always enabled foreach block coded in the IBC mode, or the mode with motion vector offsetsmay be enabled by a separate flag. If the mode with motion vectoroffsets is not enabled for the current block, the process proceeds tostep (S1308) where the current block is decoded in accordance with theIBC mode. If the mode with motion vector offsets is enabled for thecurrent block, the process proceeds to step (S1310) where the currentblock is decoded in accordance with the IBC mode and the offset. Theprocess illustrated in FIG. 13 may be terminated when one of steps(S1304), (S1308), and (S1310) is completed.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector HEVC: High Efficiency Video Coding SEI: SupplementaryEnhancement Information VUI: Video Usability Information GOPs: Groups ofPictures TUs: Transform Units, PUs: Prediction Units CTUs: Coding TreeUnits CTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

(1) A method of video decoding performed by a video decoder, the methodincluding receiving a coded video bitstream containing a currentpicture; determining whether a current block in the current picture iscoded in intra block copy (IBC) mode; in response to a determinationthat the current block is coded in IBC mode, determining whether a modewith a motion vector offset is enabled for the IBC encoded currentblock; and in response to a determination that the mode with the motionvector offset is enabled for the IBC encoded current block, decoding thecurrent block in accordance with an offset associated with the currentblock, in which fractional offsets are not permitted for the IBC encodedcurrent block.

(2) The method according to feature (1), in which the determination thatthe current block is coded in the IBC mode is based on a first flag thatindicates that the IBC mode is enabled for the current block, and inwhich in response to the determination that the first flag indicates theIBC mode is enabled for the current block, the mode with the motionvector offset is determined to be enabled for the current block.

(3) The method according to feature 2, in which in response to thedetermination that the first flag indicates the IBC mode is enabled forthe current block, the mode with the motion vector offset is determinedto be enabled for the current block and a second flag that indicateswhether fractional offsets are permitted for the mode with the motionvector offset is inferred to be false regardless of whether the secondflag is signaled.

(4) The method according to any one of features (1)-(3), in which thedetermination that the current block is coded in the IBC mode is basedon a first flag that indicates that the IBC mode is enabled for thecurrent block, and in which in response to the determination that thefirst flag indicates the IBC mode is enabled for the current block, themode with the motion vector offset is determined to be enabled for thecurrent block in response to a determination that a second flagindicates that the mode with vector offset is enabled for the currentblock.

(5) The method according to feature (4), in which in response to thedetermination that the second flag indicates that the mode with themotion vector offset is enabled for the current flag, a third flag thatindicates whether fractional offsets is enabled is inferred to be falseregardless of whether the third flag is signaled.

(6) The method according to feature (5), in which in response to adetermination that one of (i) the first flag and the (ii) second flag isfalse, the third flag that indicates whether fractional offsets isenabled is signaled.

(7) The method according to any one of features (1)-(6), in which inresponse to the determination that the mode with motion vector offset isenabled for the IBC encoded current block, the offset is selected from atable that specifies a plurality of offset distances each of which is apower of 2.

(8) A video decoder for video decoding, including processing circuitryconfigured to: receive a coded video bitstream containing a currentpicture, determine whether a current block in the current picture iscoded in intra block copy (IBC) mode, in response to a determinationthat the current block is coded in IBC mode, determine whether a modewith a motion vector offset is enabled for the IBC encoded currentblock, and in response to a determination that the mode with the motionvector offset is enabled for the IBC encoded current block, decode thecurrent block in accordance with an offset associated with the currentblock, in which fractional offsets are not permitted for the IBC encodedcurrent block.

(9) The video decoder according to feature (8), in which thedetermination that the current block is coded in the IBC mode is basedon a first flag that indicates that the IBC mode is enabled for thecurrent block, and in which in response to the determination that thefirst flag indicates the IBC mode is enabled for the current block, themode with the motion vector offset is determined to be enabled for thecurrent block.

(10) The video decoder according to feature (9), in which in response tothe determination that the first flag indicates the IBC mode is enabledfor the current block, the mode with the motion vector offset isdetermined to be enabled for the current block and a second flag thatindicates whether fractional offsets are permitted for the mode with themotion vector offset is inferred to be false regardless of whether thesecond flag is signaled.

(11) The video decoder according to feature (9), in which thedetermination that the current block is coded in the IBC mode is basedon a first flag that indicates that the IBC mode is enabled for thecurrent block, and in which in response to the determination that thefirst flag indicates the IBC mode is enabled for the current block, themode with the motion vector offset is determined to be enabled for thecurrent block in response to a determination that a second flagindicates that the mode with vector offset is enabled for the currentblock.

(12) The video decoder according to feature (11), in which in responseto the determination that the second flag indicates that the mode withthe motion vector offset is enabled for the current flag, a third flagthat indicates whether fractional offsets is enabled is inferred to befalse regardless of whether the third flag is signaled.

(13) The method according to feature (12), in which in response to adetermination that one of (i) the first flag and the (ii) second flag isfalse, the third flag that indicates whether fractional offsets isenabled is signaled.

(14) The video decoder according to any one of features (8)-(13), inwhich in response to the determination that the mode with motion vectoroffset is enabled for the IBC encoded current block, the offset isselected from a table that specifies a plurality of offset distanceseach of which is a power of 2.

(15) A non-transitory computer readable medium having instructionsstored therein, which when executed by a processor in method of videodecoding performed by a video decoder, the method including receiving acoded video bitstream containing a current picture; determining whethera current block in the current picture is coded in intra block copy(IBC) mode; in response to a determination that the current block iscoded in IBC mode, determining whether a mode with a motion vectoroffset is enabled for the IBC encoded current block; and in response toa determination that the mode with the motion vector offset is enabledfor the IBC encoded current block, decoding the current block inaccordance with an offset associated with the current block, in whichfractional offsets are not permitted for the IBC encoded current block.

(16) The non-transitory computer readable medium according to feature(15), in which the determination that the current block is coded in theIBC mode is based on a first flag that indicates that the IBC mode isenabled for the current block, and in which in response to thedetermination that the first flag indicates the IBC mode is enabled forthe current block, the mode with the motion vector offset is determinedto be enabled for the current block.

(17) The non-transitory computer readable medium according to feature(16), in which in response to the determination that the first flagindicates the IBC mode is enabled for the current block, the mode withthe motion vector offset is determined to be enabled for the currentblock and a second flag that indicates whether fractional offsets arepermitted for the mode with the motion vector offset is inferred to befalse regardless of whether the second flag is signaled.

(18) The non-transitory computer readable medium according to any one offeatures (15)-(17), in which the determination that the current block iscoded in the IBC mode is based on a first flag that indicates that theIBC mode is enabled for the current block, and in which in response tothe determination that the first flag indicates the IBC mode is enabledfor the current block, the mode with the motion vector offset isdetermined to be enabled for the current block in response to adetermination that a second flag indicates that the mode with vectoroffset is enabled for the current block.

(19) The non-transitory computer readable medium according to feature(18), in which in response to the determination that the second flagindicates that the mode with the motion vector offset is enabled for thecurrent flag, a third flag that indicates whether fractional offsets isenabled is inferred to be false regardless of whether the third flag issignaled.

(20) The non-transitory computer readable medium according to feature(19), in which in response to a determination that one of (i) the firstflag and the (ii) second flag is false, the third flag that indicateswhether fractional offsets is enabled is signaled.

What is claimed is:
 1. A method of video encoding performed by a videoencoder, the method comprising: determining whether a current block in acurrent picture is to be coded in intra block copy (IBC) mode; inresponse to determining that the current block is to be coded in the IBCmode, determining whether a mode with a motion vector offset is enabledfor the current block; in response to determining that the mode with themotion vector offset is enabled for the current block, encoding thecurrent block in accordance with an offset associated with the currentblock; and generating a coded video bitsteam based on the encodedcurrent block, wherein fractional offsets are not permitted for thecurrent block irrespective of whether a first flag that indicateswhether fractional offsets are permitted for the mode with the motionvector offset is a value permitting fractional offsets, wherein, inresponse to a determination that the motion vector offset is afractional offset, the motion vector offset is left shifted such thatthe motion vector offset is converted from the fractional offset to aninteger offset.
 2. The method according to claim 1, wherein thedetermination that the current block is to be coded in the IBC mode isbased on a second flag that indicates that the IBC mode is enabled forthe current block, and wherein in response to the determination that thesecond flag indicates that the IBC mode is enabled for the currentblock, the mode with the motion vector offset is determined to beenabled for the current block.
 3. The method according to claim 1,wherein the determination that the current block is coded in the IBCmode is based on a second flag that indicates that the IBC mode isenabled for the current block, and wherein in response to thedetermination that the second flag indicates that the IBC mode isenabled for the current block, the mode with the motion vector offset isdetermined to be enabled for the current block in response to adetermination that a third flag indicates that the mode with vectoroffset is enabled for the current block.
 4. The method according toclaim 3, wherein in response to the determination that the third flagindicates that the mode with the motion vector offset is enabled for thecurrent block, the first flag that indicates whether fractional offsetsare permitted is set to false irrespective of whether the first flag isthe value permitting fractional offsets.
 5. The method according toclaim 4, wherein in response to a determination that one of (i) thethird flag and the (ii) second flag is false, the first flag thatindicates whether fractional offsets is enabled, and is signaled in thecoded video bitstream.
 6. The method according to claim 1, wherein inresponse to the determination that the mode with motion vector offset isenabled for the IBC encoded current block, the offset is selected from atable that specifies a plurality of offset distances each of which is apower of
 2. 7. A video encoder for video encoding, comprising:processing circuitry configured to determine whether a current block inthe current picture is to be coded in intra block copy (IBC) mode, inresponse to a determination that the current block is coded in the IBCmode, determine whether a mode with a motion vector offset is enabledfor the IBC encoded current block, in response to a determination thatthe mode with the motion vector offset is enabled for the IBC encodedcurrent block, encode the current block in accordance with an offsetassociated with the current block, and generate a coded video bitsteambased on the encoded current block, wherein fractional offsets are notpermitted for the IBC encoded current block irrespective of whether afirst flag that indicates whether fractional offsets are permitted forthe mode with the motion vector offset is a value permitting fractionaloffsets, and wherein, in response to a determination that the motionvector offset is a fractional offset, the motion vector offset is leftshifted such that the motion vector offset is converted from thefractional offset to an integer offset.
 8. The video encoder accordingto claim 7, wherein the determination that the current block is to becoded in the IBC mode is based on a second flag that indicates that theIBC mode is enabled for the current block, and wherein in response tothe determination that the second flag indicates that the IBC mode isenabled for the current block, the mode with the motion vector offset isdetermined to be enabled for the current block.
 9. The video encoderaccording to claim 8, wherein the determination that the current blockis coded in the IBC mode is based on a second flag that indicates thatthe IBC mode is enabled for the current block, and wherein in responseto the determination that the second flag indicates that the IBC mode isenabled for the current block, the mode with the motion vector offset isdetermined to be enabled for the current block in response to adetermination that a third flag indicates that the mode with vectoroffset is enabled for the current block.
 10. The video encoder accordingto claim 9, wherein in response to the determination that the third flagindicates that the mode with the motion vector offset is enabled for thecurrent block, the first flag that indicates whether fractional offsetsare permitted is set to false irrespective of whether the first flag isthe value permitting fractional offsets.
 11. The video encoder accordingto claim 10, wherein in response to a determination that one of (i) thethird flag and the (ii) second flag is false, the first flag thatindicates whether fractional offsets is enabled, and is signaled in thecoded video bitstream.
 12. The video encoder according to claim 7,wherein in response to the determination that the mode with motionvector offset is enabled for the IBC encoded current block, the offsetis selected from a table that specifies a plurality of offset distanceseach of which is a power of
 2. 13. A non-transitory computer readablemedium having instructions stored therein, which when executed byprocessing circuitry, cause the processing circuitry perform a method ofvideo encoding, the method comprising: determining whether a currentblock in a current picture is to be coded in intra block copy (IBC)mode; in response to determining that the current block is to be codedin the IBC mode, determining whether a mode with a motion vector offsetis enabled for the current block; in response to determining that themode with the motion vector offset is enabled for the current block,encoding the current block in accordance with an offset associated withthe current block; and generating a coded video bitsteam based on theencoded current block, wherein fractional offsets are not permitted forthe current block irrespective of whether a first flag that indicateswhether fractional offsets are permitted for the mode with the motionvector offset is a value permitting fractional offsets, wherein, inresponse to a determination that the motion vector offset is afractional offset, the motion vector offset is left shifted such thatthe motion vector offset is converted from the fractional offset to aninteger offset.
 14. The non-transitory computer readable mediumaccording to claim 13, wherein the determination that the current blockis to be coded in the IBC mode is based on a second flag that indicatesthat the IBC mode is enabled for the current block, and wherein inresponse to the determination that the second flag indicates that theIBC mode is enabled for the current block, the mode with the motionvector offset is determined to be enabled for the current block.
 15. Thenon-transitory computer readable medium according to claim 13, whereinthe determination that the current block is coded in the IBC mode isbased on a second flag that indicates that the IBC mode is enabled forthe current block, and wherein in response to the determination that thesecond flag indicates that the IBC mode is enabled for the currentblock, the mode with the motion vector offset is determined to beenabled for the current block in response to a determination that athird flag indicates that the mode with vector offset is enabled for thecurrent block.
 16. The non-transitory computer readable medium accordingto claim 15, wherein in response to the determination that the thirdflag indicates that the mode with the motion vector offset is enabledfor the current block, the first flag that indicates whether fractionaloffsets are permitted is set to false irrespective of whether the firstflag is the value permitting fractional offsets.
 17. The non-transitorycomputer readable medium according to claim 16, wherein in response to adetermination that one of (i) the third flag and the (ii) second flag isfalse, the first flag that indicates whether fractional offsets isenabled, and is signaled in the coded video bitstream.